NCCAA Re-certification Practice Exam

The correct answer focuses on the initial phase of terminating norepinephrine's effects at the receptor site, which begins with the diffusion of norepinephrine away from the receptor. Once norepinephrine has been released into the synaptic cleft, it binds to adrenergic receptors to exert its physiological effects. For these effects to stop, the molecule must first disengage from the receptor, which occurs mainly through diffusion. After this initial diffusion, other processes come into play, such as reuptake into the nerve terminal, where norepinephrine can be repackaged or metabolized, and enzymatic breakdown through monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT). However, the very first action that takes place in the termination process is that norepinephrine moves away from its receptor site, which sets the stage for its subsequent clearance from the synaptic space.